碰撞造山带地壳深熔作用:来自纳米花岗岩包裹体的观测与实验约束

在碰撞造山带构造演化过程中，中下地壳深熔作用对于深部地壳物理性质与化学成分具有重要控制作用.作为深熔作用的"见证者"，纳米花岗岩包裹体是寄主岩石部分熔融作用的产物，能够为确定陆壳岩石中天然熔体特征及分析熔融机制提供关键信息.在喜马拉雅东构造结南迦巴瓦岩群的代表性岩石单元（泥质片麻岩与长英质片麻岩）中，石榴石与锆石中常包含有典型的纳米花岗岩包裹体，其代表性子矿物组合为钾长石+斜长石+石英±黑云母，这是在黑云母脱水熔融过程中、寄主片麻岩中熔体被主要转熔矿物（如石榴石等）捕获所形成一类特殊包裹体.在观测基础上，采用高温高压与高温常压手段，对纳米花岗岩包裹体进行均一化实验并获得均一化玻璃质熔体.成分分析表明，均一化熔体成分以过铝质花岗岩为主，其主/微量元素特征能够有效反演部分熔融作用的演化过程.因此，纳米花岗岩包裹体的天然观测与实验研究对于确定天然熔体特征与深入剖析碰撞造山带的地壳深熔作用具有重要启示意义. 

Crust Anatexis in Collisional Orogenic Belt: Constraints from Natural Observations and Experimental Investigation on Nanogranite Inclusions

Crustal anatexis during the tectonic evolution of collisional orogenic belts has a fundamental impact on physical properties and chemical compositions of the deep crust. As the direct witness to crustal anatexis, nanogranite inclusions, which formed during partial melting of hosted crustal rocks, are key to determine the compositions of the natural melts as well as melting mechanism. Nanogranite inclusions within garnet and zircon were identified in pelitic gneisses and felsic gneisses from the Namche Barwa complex of the eastern Himalayan syntaxis. They have a typical granitic mineral assemblage of K-feldspar, plagioclase, and quartz with or without biotite. These minerals represent the former melt as a result of dehydration melting of biotite in gneisses, which is captured by peritectic minerals (like garnet). Homogenization experiments on the nanogranite inclusions were conducted under high temperature and pressure and high temperature and room pressure conditions in order to obtain homogenized glasses. Chemical analyses show that these homogenized glasses are dominated by peraluminous granites. The major-and trace-element compositions of these glasses can be used to trace the melting processes of the host rocks. A combination of natural observation and experimental investigation of nanogranite inclusions from collisional orogenic belts is crucial to gain further insights into the crustal anatexis and associated melt compositions.